"These findings provide us with a much better understanding of how this class of drugs may act upon the brain in ways that might raise the risk of cognitive impairment and dementia," says Shannon Risacher. "Physicians might want to consider alternatives to anticholinergic medications if available when working with their older patients." (Credit: iStockphoto)

Older adults might want to avoid a using class of drugs commonly found in over-the-counter products such as nighttime cold medicines. A new study shows they are linked to cognitive impairment.

Using brain imaging techniques, researchers found lower metabolism and reduced brain sizes among study participants taking the drugs known to have an anticholinergic effect, meaning they block acetylcholine, a nervous system neurotransmitter.

Previous research found a link between the anticholinergic drugs and cognitive impairment and increased risk of dementia. The new paper published in the journal JAMA Neurology is believed to be the first to study the potential underlying biology of those clinical links using neuroimaging measurements of brain metabolism and atrophy.

“These findings provide us with a much better understanding of how this class of drugs may act upon the brain in ways that might raise the risk of cognitive impairment and dementia,” says Shannon Risacher, assistant professor of radiology and imaging sciences at Indiana University.

“Given all the research evidence, physicians might want to consider alternatives to anticholinergic medications if available when working with their older patients.”

Drugs with anticholinergic effects are sold over the counter and by prescription as sleep aids and for many chronic diseases including hypertension, cardiovascular disease, and chronic obstructive pulmonary disease.

Scientists have linked anticholinergic drugs cognitive problems among older adults for at least 10 years. A 2013 study found that drugs with a strong anticholinergic effect cause cognitive problems when taken continuously for as few as 60 days. Drugs with a weaker effect could cause impairment within 90 days.

Worse short-term memory

The current study involved 451 participants, 60 of whom were taking at least one medication with medium or high anticholinergic activity. The participants were drawn from a national Alzheimer’s research project—the Alzheimer’s Disease Neuroimaging Initiative—and the Indiana Memory and Aging Study.

To identify possible physical and physiological changes that could be associated with the reported effects, researchers assessed the results of memory and other cognitive tests, positron emission tests (PET) measuring brain metabolism, and magnetic resonance imaging (MRI) scans for brain structure.

The cognitive tests revealed that patients taking anticholinergic drugs performed worse than older adults not taking the drugs on short-term memory and some tests of executive function, which cover a range of activities such as verbal reasoning, planning, and problem solving.

Anticholinergic drug users also showed lower levels of glucose metabolism—a biomarker for brain activity—in both the overall brain and in the hippocampus, a region of the brain associated with memory and which has been identified as affected early by Alzheimer’s disease.

The researchers also found significant links between brain structure revealed by the MRI scans and anticholinergic drug use, with the participants using anticholinergic drugs having reduced brain volume and larger ventricles, the cavities inside the brain.

“These findings might give us clues to the biological basis for the cognitive problems associated with anticholinergic drugs, but additional studies are needed if we are to truly understand the mechanisms involved,” Risacher says.

Other researchers from Indiana University and from the University of California, Berkeley; the University of Washington; the University of Southern California; the University of California, San Diego; the University of California, San Francisco; and the Mayo Clinic are coauthors of the study.

The Alzheimer’s Disease Neuroimaging Initiative and the Department of Defense funded the work.